Originally Posted by curious_miles

Big negative balance is a red flag, small ones are ok.
When you send a check for payment, they credit your account on the day they received your check, and what if the check bounces? Amex and BofA are very sensitive to this and will subject your case to a manual review, citi has been more tolerant to this, but there are reports that citi doesn't welcome it either. You will come out clean at the end because you didn't do anything wrong, but why make it smell like a money laundering?

Just give a call and ask for a limit raise, it's a good opportunity to increase your credit limit and this will make you look good as well on the credit report.